I've been thinking about grand strategy games recently, and it occurs to me that supply rules are a lot like encumbrance rules, in that they're a pain in the ass but also worthwhile because they convey the same concerns the character experiences up to the player. A dungeoneer worries about how much weight he's carrying; a general worries about how to keep his men fed. What's more, as Keegan's History of Warfare suggests, supply concerns dictated the largely-coastal structures of campaigns in the Hellenic era. Without supply, you get all kinds of crazy long-term unsupported actions in the enemy rear (this is a problem I have observed in, say, the Civilization series of games).
But the difference between supply and encumbrance is that we're reached a reasonablish compromise between complexity and realism in our encumbrance rules, with encumbrance by stone or with Traveller's low-kilos threshold. I don't know if supply is amenable to simplication... but until I find a set of rules for it which are really light-weight, I expect that it will remain one of those much-begrudged rules which is ignored by the players whenever I forget about it.
(Been thinking about wargame campaigns again, since I'm back in Collegetown and one of my main wargaming opponents / buddies is still around)